HI Ron
Graeme Wright's book, 3rd edition, does indeed have reloading info for the 375 flanged---see pages 110 and 111---most of the powders he quotes are available in the US and Canada. I have used his recipes, albeit carefully. The trick as you know is to get a load that regulates for your rifle. If I can be of more assistance, send me a PM.
Regards
Bill